The following document lists the file abstract/TPHILLIP_TGP_OI.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
We propose to use ISO observations of the 63 micron line of OI to
determine the gas phase oxygen abundance in dense interstellar
clouds, where complex molecules are found and where the interstellar
UV radiation field is attenuated by dust. It has been shown that
carbon can be largely accounted for by CO and CI measurements,
but the predicted molecular reservoirs of oxygen, O_{2} and H_{2}O,
have been shown not to account for the anticipated gas phase oxygen
by at least an order of magnitude. We expect that the remainder is
largely atomic oxygen and propose a method of 63 micron absorption
spectroscopy to identify the missing oxygen content of these clouds.
In order to separate OI emission from the background continuum source
from OI absorption by the foreground source we select lines of sight
where the velocity separation of emitter and absorber is greater
than the LWS resolution of 30 km/s. Also, to avoid the effects of
strong PDRs we choose absorbing clouds well removed from ionizing
stars. Further, to aid in the understanding of the relation between
the oxygen generated in the PDRs at the cloud surfaces, caused by
the ambient interstellar UV field, and oxygen associated with the
more shielded molecular region, we measure a set of clouds with a
range of H_{2} column densities. The cloud OI absorption should
correlate with the H_{2} column densities (determined from trace
molecules), whereas the PDR contribution should be roughly a
constant.